This application claims benefit of Japanese Patent Application No. H11-182331 filed in Japan on Jun. 28, 1999, the contents of which are incorporated by this reference.
1. Field of the Invention
This invention relates to a flash light emitting device, and more particularly to a flash light emitting device equipped with a charge device.
2. Related Art Statement
Conventionally, in the field of flash light emitting devices used for photographing with cameras or the like, to measure a charge voltage of a capacitor which stores the light emitting energy, a method in which a plurality of resistors are provided at both ends of the capacitor and the voltage of the capacitor is measured based on voltages generated to division resistors at the time of operating a charge circuit has been proposed.
Further, an aluminum electrolytic capacitor is used as the capacitor which stores the energy.
In such flash light emitting devices, however, at the time of measuring the charge voltage, the charging of short time inevitably becomes necessary before the measurement of the capacitor voltage. In case the turning on and off of a photographing preparation switch (a first release of the release of the camera) is repeated due to such a measurement mode, the measurement of the charge voltage of the capacitor is performed each time the switch is turned on and hence, the voltage of the capacitor is increased and exceeds a given charge voltage. Accordingly, a drawback that an amount of light which exceeds a given amount of light is generated at the time of strobe light emission or the charge voltage is increased and exceeds the withstand voltage of the capacitor may arise.
Further, the aluminum electrolytic capacitor which is used as the charging capacitor is liable to increase the leakage of the charge when the voltage is increased or the temperature is elevated.
FIG. 10 shows an equivalent circuit of a typical aluminum electrolytic capacitor. According to this equivalent circuit shown in FIG. 10, a variable resistor which varies its resistance due to voltage and temperature is connected to both ends of the capacitor. In such a charge storing capacitor, the charge leaks during charging and hence, unless the charge which exceeds the necessary charge amount is supplied to the capacitor, there arises a problem that the voltage of the capacitor does not reach the full charge voltage.
Here, the difference between the aluminum electrolytic capacitor and a film capacitor is explained.
In the aluminum electrolytic capacitor, a dielectric is made of aluminum oxide (Al2O3), while in the film capacitor, a dielectric is made of polyester, polypropylene or the like.
To be more specific, in the aluminum electrolytic capacitor, the dielectric is formed such that an aluminum foil which is subjected to an etching treatment is continuously electrochemically treated in a liquid made of ammonium pentaborate or the like at a voltage (formation voltage) which is 120-200% of the rated voltage. The advantage of the aluminum electrolytic capacitor lies in the low cost, the compactness and the large capacity.
The film capacitor is constituted as follows. That is, a film which deposits aluminum onto a polyester (PET), polypropylene (OPP) or polyphenylene sulfide (PPS) film by a vacuum deposition is used as the dielectric. The film is wound while assuring the insulation between film and aluminum. Metallikons are provided to both ends of the film to form the non-inductive structure. Lead wires are welded to the metallikon portions and an outer casing is provided around the wound film. The advantage of the film capacitor lies in the excellent characteristics, the extent that the capacitor can be manufactured from low voltage to high voltage and the high reliability.
FIG. 11 is a diagram which shows the consumed current amount of a boosting circuit necessary for boosting a unit voltage of a typical aluminum electrolytic capacitor and a film capacitor. As shown in FIG. 11, it is understood that corresponding to the increase of voltage, the necessary charge amount of the aluminum electrolytic capacitor is increased.
FIG. 12 is a diagram showing the lapse of time of holding voltage of a typical aluminum electrolytic capacitor and a film capacitor. As shown in FIG. 12, it is understood that when the voltage is high, the lowering of voltage of the aluminum electrolytic capacitor is sharp and hence, the charge which has been stored is lost wastefully. Accordingly, a problem that the aluminum electrolytic capacitor must be recharged right before charging arises.
It is the first object of the present invention to provide a flash light emitting device which can properly perform a charge control of a main capacitor and prevent a wasteful consumption of the energy.
It is the second object of the present invention to provide a flash light emitting device which can prevent the charge voltage of the capacitor from exceeding the full charge voltage even when the turning on and off of a photographing preparation switch is repeated many times and obviates the consumption of the wasteful energy.
To summarize the present invention, in the flash light emitting device which includes a charging circuit for charging the light emitting energy into a capacitor by boosting a power supply voltage and a light emitting circuit for making a flash light emitting tube emit light with the use of the energy of the capacitor, the flash light emitting device further includes timer means which counts a lapsed time from a point of time that a given amount of charging to the capacitor performed by the charging circuit is completed and charging control means which controls whether a next charging operation by the charging circuit is to be star ted or not based on the lapsed time counted by the timer means.
These objects and advantages of the present invention will become further t from the following detailed explanation.